"Quantification and impact of nonparabolicity of the conduction band of indium tin oxide on its plasmonic properties"

Xiaoge Liu: Junghyun Park, Ju-Hyung Kang, Hongtao Yuan, Yi Cui, Harold Y. Hwang and Mark L. Brongersma; Applied Physics Letters, 11/03/14.

Additional Authors: Junghyun Park, Ju-Hyung Kang, Hongtao Yuan, Yi Cui, Harold Y. Hwang and Mark L. Brongersma

Abstract:

Doped indium tin oxide (ITO) behaves as a Drude metal with a plasma frequency that is controlled by its free carrier density. In this work, we systematically tune this frequency across the mid-infrared range by annealing treatments in a reducing environment that produce high electron concentrations (∼1021 cm−3). The changes in ITO’s optical properties that result from the changes in carrier density are measured by attenuated total reflection measurements. These optical frequency measurements are complemented by Hall measurements to obtain a comprehensive picture of the Drude response of the ITO films. It was found that a complete description of the optical properties at very high carrier densities needs to account for the nonparabolicity of the conduction band of ITO and a reduced carrier mobility. More specifically, an increase in carrier concentration from 6.2 × 1019 cm−3 to 1.4  x 1021 cm−3 comes with a change of the effective electron mass from 0.35  to 0.53 and a decrease in the optical frequency mobility from about 20 cm2 V−1 s−1 to 9 cm2 V−1 s−1.